Can be used more than once in a turn. Each time, the opponent can pay to prevent giving first strike to a creature, but this payment only stops the current activation and not future activations of Tidal Flats.

10/4/2004

The payment is made when the Tidal Flats effect resolves.

10/4/2004

First Strike is granted to your creatures currently blocking non-Flyers when this effect resolves.